1. Field of the Invention
The present invention relates to the field of radiation beam focusing and, more specifically, an embodiment of the present invention relates to a method and a system for the two-dimensional collimation of an x-ray beam.
2. Background of the Invention.
Accelerator-produced high-energy x-ray beams often must be collimated to produce a narrow beam having parallel planar boundaries.
In most situations, a large fraction of the beam incident on the collimator must be blocked by the collimator. This results in large amounts of heat being deposited in the collimator which requires a means to carry heat away from the collimator.
Sometimes it is necessary to install separate collimators with plates that narrow a beam (initially traveling, say, in the z direction) first in the x direction and then in the y direction (or in any two orthogonal directions) so as to allow adjustment of the separation between the plates. This sequential arrangement requires the sacrifice of valuable space in the experimental area, space that can otherwise be populated by instruments and components to enhance research.
Slits are widely used throughout the Advanced Photon Source beam lines at Argonne National Laboratory (Argonne, Ill.), and other x-ray facilities around the world, to both define the size of the x-ray beam and to vary the overall heat load on downstream optical components. White beam slits in particular, require cooled beam absorbing surfaces, to intercept the beam at some incident angle determined by the beam profile. As this angle gets smaller, the mask must get longer to maintain the same effective inlet aperture. There are many different designs in operation and in most cases, a single x-ray beam requires the opposing horizontal and vertical edges of two separate mask bodies to define it.
A typical beamline has one or two undulators installed inline at the straight section between bending magnets in the accelerator storage ring. A canted undulator beamline uses additional magnets to cant the electrons 5 mrad outboard through the first undulator, then inboard 1 mrad through the second undulator which creates two independent beams 1 mrad apart. A third corrector magnet steers the electrons back into the storage ring.
To define the beam in both the horizontal and vertical, an L-type design is typically employed. These slits are basically comprised of a pair of movable masks, in line with the beam, that work together. Each mask will define one horizontal and one vertical beam edge. In many cases, these mask bodies are identical, with one flipped upside down in relation to the other to define opposing edges.
The problem with this traditional design is that each beam requires two masks separated by a bellows to allow for independent motion. In the case of a canted undulator beamline, the independent manipulation of both beams would require four separate masks which would eat up a large portion of valuable beamline real estate.
A need exists in the art for a method and a system for independently varying each beam of a multi radiation beam line. For example, in a dual beam line geometry, the method and system should allow for varying the size of one electron beam while allowing the second beam to pass through unaffected. The method and system should be compact compared to traditional designs. Also, the method and system should involve no moving slits relative to each other so as to minimize maintenance and alignment issues.